Mistake: Degrees all the same
As mentioned in the instructions for the exercise, give your ellipses a bit of a shift in their degree as you run through the length of the form.
The reason for this is explained in the little exaggerated red doodle. When you have an object held in front of you and you take three parallel slices of it, your viewing angle for each slice is going to be different. If it's dead center in front of you, you're not going to be able to see any of its face, just its edge. If it's off to the side, you'll see a little more of it.
Now because the size of sausage form is actually quite small, the shift isn't going to be that significant (unless the form itself is bending, which it may well be). All the same, you're not going to end up in a situation where the degrees are all the same.
... At least not unless it's bending backwards in just the perfect amount but we're not going to get into that.